The present invention relates to injection molding apparatus and procedures and more particularly to a structure and method for enabling and facilitating the transmission of information from injection mold sensors to a control device and in response to the signals from the mold sensors the control device transmits information to the mold without the use of cumbersome and expensive analog hard-wired connections. The present invention also provides increased reliability in the feedback control loop as it enables the user to eliminate numerous junctions which can introduce errors into the control system.
Injection molding is typically done in molds which operate at high temperatures and high pressures within the molds. Typical molds include means-to heat the molds at numerous points within the mold in order to ensure that the material injected into the mold remains in a molten state until the mold cavity is completely filled and that no voids exist within the cavity (i.e. hot runner system) as is known to those skilled in the art. In addition, as is known to those skilled in the art, it can be desirable to heat a mold, prior to injecting material therein, in order to control the rate at which the material cools and hardens in order to effect the material properties of the molded product (e.g. material strength, etc.)
In order to effect such control, it is necessary to provide a closed-loop feedback system between the controlled device (e.g., a mold heater) and the mold sensor (e.g., a mold temperature sensor), through a controller of some sort which can utilize the information from the mold sensor and control the controlled device in accordance with a predetermined set of instructions. Currently, information from injection mold sensors is transmitted to a controller in analog form via a hard-wired connection which utilizes sensor specific wires which are physically connected to the sensors and the control device through a series of connectors. These wires, used with readily available connectors, create sensor feedback cables. Each cable typically requires two or more wires per sensor located in the mold to transfer an analog signal.
The number of cables required to transfer the information as applied to, for example, temperature in thermal analog form, from the mold to the control device, is dependent on the number of sensor devices located in the mold, but often times exceeds 48 wires for a typical commercial mold configuration. For example, if a mold requires 30 sensor devices, 60 analog sensor wires would typically be required. In addition, each of the sensor wires is typically arranged such that there are 7 thermal junction points between the sensor device and the control device for each sensor wire. Accordingly, in an injection mold such as the one described above, there would be 420 connections created between the sensor devices in the identified mold and the control device for that mold.
Closed-loop feedback systems such as those described above with numerous wires and connectors can create various problems known to those skilled in the art, including: 1) problems associated with bad connections and cold solder joints which may feedback faulty or intermittent data; 2) inaccurate feedback due to temperature variations along the path of the analog feedback cable; 3) the effects of electrical noise on low level analog signals over the span of the feedback cable; 4) numerous problems caused by the sheer volume of cables and wires required, including problems as simple as storage of the wires and-cables, and people tripping over cables located on the floor of the injection mold area; and 5) other problems known to those skilled in the art. As the number of sensors in a given mold increases, so too does the number of wires and connections in a conventional system. Thus, as the mold becomes more intricate or sophisticated and control of the operation of the mold becomes more critical, the chance for induced error in a conventional control system similarly increases indeed, one practical limitation on the number of temperature sensors which can be effectively employed in injection molding systems results from the limitation on the number of sensor and control wires which a system and system operator can manage.
The preferred embodiment of the present invention provides for sensor input circuitry to be positioned within a thermally isolated enclosure attached to the mold or positioned in the vicinity of the mold. A signal processor, which in the preferred embodiment of the present invention converts analog sensor signals from the sensors into a digital format is also provided. Sensors may be provided to monitor, set point, actual mold temperature, power output, or any other parameter of interest to the mold operator. In addition, the present invention includes a communicator positioned within the thermally isolated enclosure to transmit information from the various mold sensors, once it has been converted to digital format, to the mold controller and a receiver positioned in or in the proximity of the mold controller to receive said digital information transmitted to the mold controller from the communicator so as to permit the closed-loop control of the molding apparatus. The information may be transmitted by means of digital wire, RF (radio frequency) or IR (infrared).
An advantage of the invention is that, unlike the system of the prior art which required numerous analog connections and the concomitant problems associated therewith, the present invention allows the transmission of signals from the sensor input circuitry to the mold controller to be accomplished by digital means, thereby eliminating numerous analog connections and the associated problems therewith. The present invention also allows for the transmission of control signals from the mold controller or operator interface back to the mold so as to provide for an automatic closed-loop control system. This digital interface eliminates all but one of the analog connections, thereby almost entirely eliminating the possibility of junction induced error.
In addition, because the information is preferably converted to digital form within a thermally isolated enclosure located on the proximity of the mold itself and transmitted in such form to the control device, the possibility of electrical noise effecting an analog control signal is also greatly reduced. Furthermore, many advantages are created through the elimination of the numerous cables required by the prior art, including: 1) reduced replacement costs for the numerous wires; 2) reduction in cable connection errors; 3) energy a and space savings due to the elimination of the need to transport and store the vast number of wires and cables required under the prior art; 4) elimination of the safety hazard created when low level analog signals run next to high power output cables, which may be mistakenly connected to the wrong device and cause damage, fire or electrocution; and 5) elimination of the safety hazard created when numerous wires and cables are run along the floor of the area in which the injection mold is positioned.
An additional feature of an alternate embodiment of this invention is the providing of a quick connect/disconnect apparatus for attaching the enclosure to the mold. A junction box is provided on the mold allows for the quick and easy connection of the thermally isolated enclosure. The enclosure may be removed and the prior standard analog cables attached if for whatever reason the operator wishes to switch back to the prior technology. Also, the easy removal of the enclosure allows for its easy substitution and replacement if needed.
These and other features and advantages of the present invention will become apparent from the following detailed description of a preferred embodiment which, taken in conjunction with the accompanying drawings, illustrates by way of example the principles of the invention.